Radiation curable thermal transfer elements

ABSTRACT

Radiation curable thermal transfer elements including a substrate and a light-to-heat conversion layer overlaying the substrate, and processes to make the thermal transfer elements. The light-to-heat conversion layer is derived from a radiation curable material capable of being cured by exposure to radiation at a curing wavelength and an imaging radiation absorber material not substantially increasing radiation absorbance at the curing wavelength. The radiation curable transfer elements can be used in processes for making organic microelectronic devices.

FIELD OF INVENTION

The present invention relates to thermal transfer elements, particularlyto radiation curable thermal transfer elements useful in laser inducedthermal imaging (LITI) or other imaging processes. The present inventionfurther relates to methods for fabricating and using radiation curedthermal transfer elements to fabricate organic microelectronic devices.

BACKGROUND

Many miniature electronic and optical devices are formed using layers ofdifferent materials stacked on each other. Examples of such devicesinclude optical displays in which each pixel is formed in a patternedarray, optical waveguide structures for telecommunication devices, andmetal-insulator-metal stacks for semiconductor-based devices. Aconventional method for making these devices includes forming one ormore layers on a receptor substrate and patterning the layerssimultaneously or sequentially to form the device. Patterning of thelayers is often performed by photolithographic techniques that include,for example, covering a layer with a photoresist, patterning thephotoresist by exposure to radiation through a mask, removing a portionof either the exposed or non-exposed photoresist to reveal theunderlying layer according to the pattern, and then etching the exposedlayer.

In many cases, multiple deposition and patterning steps are required toprepare the ultimate device structure. For example, the preparation ofoptical displays may require the separate formation of red, green, andblue pixels. Although layers may be commonly deposited for each of thesetypes of pixels, some layers must be separately formed and oftenseparately patterned. In some applications, it may be difficult orimpractical to produce devices using conventional photolithographicpatterning. There is thus a need for new methods of forming thesedevices. In at least some instances, this may allow for the constructionof devices with more reliability and more complexity.

LITI has been developed as an alternative patterning method formultilayer microelectronic and optical devices. LITI is a digitalpatterning method involving the transfer of materials from a donor sheetto a receptor surface. LITI methods generally include pattern-wiseprinting of one or more transfer layers for display applications. LITIpatterning methods typically use a multi-layer thermal transfer donorfilm that is pattern-wise exposed by a source of radiation (e.g., aninfrared laser or flashlamp exposing through a mask) to transfer apatterned transfer layer from the donor film to a desired substrate.

SUMMARY

A first embodiment includes a radiation curable thermal transfer elementincluding a substrate and a light-to-heat conversion (LTHC) layeroverlaying the substrate. The LTHC layer is derived from a radiationcurable material capable of being cured by exposure to radiation at acuring wavelength or wavelengths, and an imaging radiation absorbermaterial that does not substantially increase radiation absorption atthe curing wavelength or within the range of curing wavelengths.

A second embodiment includes a radiation curable thermal transferelement including a substrate and an LTHC layer overlaying thesubstrate. The LTHC layer contains a radiation curable material capableof being cured by exposure to radiation at a curing wavelength orwavelengths, and an imaging radiation absorber material which does notsubstantially increase radiation absorption at the curing wavelength orwithin the range of curing wavelengths prior to curing of the radiationcurable material.

A third embodiment includes a thermal transfer element cured by exposureto radiation at a curing wavelength or wavelengths and including asubstrate and an LTHC layer overlaying the substrate. The LTHC layer isderived from a radiation curable material and an imaging radiationabsorber material which does not substantially increase radiationabsorption at the curing wavelength or within the range of curingwavelengths. The amount of residual curable material is substantiallyless than the amount of residual curable material present in a thermaltransfer element having comparable imaging radiation absorption andthickness in which the imaging radiation absorber material is replacedwith a small particle absorber material cured under the same conditions.

A fourth embodiment includes a thermal transfer element cured byexposure to radiation at a curing wavelength or wavelengths andincluding a substrate and an LTHC layer overlaying the substrate. TheLTHC layer is derived from a radiation curable material and an imagingradiation absorber material which does not substantially increaseradiation absorption at the curing wavelength or within the range ofcuring wavelengths. The amount of residual curable material issubstantially less than the amount of residual curable material presentin a thermal transfer element including a small particle absorbermaterial.

A fifth embodiment includes a process for making a thermal transferelement including a substrate and an LTHC layer overlaying the substrateand derived from a radiation curable material and an imaging radiationabsorber material which does not substantially increase radiationabsorption at a curing wavelength or wavelengths, including the steps ofcoating the LTHC layer on the substrate, and curing the radiationcurable material such that the imaging radiation absorber material doesnot substantially increase radiation absorption at a curing wavelengthor within the range of curing wavelengths.

A sixth embodiment includes a process for making an organicmicroelectronic device including the steps of providing a thermaltransfer element including a substrate and an LTHC layer overlaying thesubstrate, the LTHC derived from a radiation curable material capable ofbeing cured by exposure to radiation at a curing wavelength orwavelengths, and an imaging radiation absorber material which does notsubstantially increase radiation absorption at the curing wavelength orwithin the range of curing wavelengths; placing the thermal transferelement and a receptor in intimate contact; exposing the thermaltransfer element in an image-wise pattern with a source of near infraredradiation; and transferring at least a portion of the thermal transferelement corresponding to the image-wise pattern to the receptor to forman organic microelectronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in the followingdetailed description of various embodiments of the invention inconnection with the accompanying drawings, in which:

FIG. 1 is a cross-sectional diagram illustrating an exemplary LITI donorfilm construction;

FIG. 2A is a graph illustrating a spectrum of Prussian Blue (Penn Color)in an LTHC layer;

FIG. 2B is a graph illustrating a spectrum of Pro-Jet 830 LDI (Avecia)in an LTHC layer; and

FIG. 2C is a graph illustrating a spectrum of YKR 2900 (Yamamoto) in anLTHC layer.

DETAILED DESCRIPTION

The present specification relates to patterning methods for LITItransfer layers used in LITI donor films. The LITI donor films may beused in the formation or partial formation of devices and other objectsusing thermal transfer and thermal transfer elements for forming thedevices or other articles. As a particular example, a thermal transferelement can be formed for making, at least in part, a multilayer device,such as a multilayer active device and passive device, for example asmultilayer electronic and optical devices. This process can beaccomplished, for example, by thermal transfer of a multi-componenttransfer assembly from a thermal transfer element to a final receptor.It will be recognized that single layer and other multilayer transferscan also be used to form devices and other articles.

An order in the present specification (e.g., an order of steps to beperformed or an order of layers on a substrate) is not meant to precludeintermediates between the items specified. Furthermore, as used herein:

The term “active device” includes an electronic or optical componentcapable of a dynamic function, such as amplification, oscillation, orsignal control, and may require a power supply for operation.

The term “curing wavelength” includes a wavelength or range ofwavelengths that upon absorption within the LTHC layer is capable ofinitiating polymerization and/or crosslinking of the radiation curablematerial.

The term “imaging wavelength” includes a wavelength or range ofwavelengths emitted by the imaging source.

The term “microelectronic device” includes an electronic or opticalcomponent that can be used alone and/or with other components to form alarger system, such as an electronic circuit.

The term “passive device” includes an electronic or optical componentthat is basically static in operation (i.e., it is ordinarily incapableof amplification or oscillation) and may require no power forcharacteristic operation.

The term “small particle absorber” includes an absorber that providesfor absorption and scattering of light by small particles as describedin, for example, the following text: C. F. Bohren and D. R. Huffman,Absorption and Scattering of Light by Small Particles, John Wiley &Sons, Inc., Library of Congress ISBN 0-471-29340-7 (1983), incorporatedherein by reference.

Thermal Transfer Elements

The present invention provides LITI donor films including radiationcurable thermal transfer elements and methods of preparing radiationcured thermal transfer layers useful in fabricating microelectronic andoptical devices, for example. As shown in FIG. 1, an exemplary LITIdonor film includes a donor substrate 100 for mechanical support and anLTHC layer 102 overlaying the substrate 100 and used for transformingimaging power into heat. Other layers may include, for example, atransfer layer 106, an optional interlayer 104 overlaying the substrate,an optional underlayer 108 interposed between the substrate 100 and theLTHC layer 102, and an optional release layer 110 underlying thetransfer layer.

Substrate and Optional Primer Layer

Generally, the LITI donor thermal transfer element includes a substrate.The donor substrate can be a polymer film. One suitable type of polymerfilm is a polyester film, for example, polyethylene terephthalate (PET)or polyethylene naphthalate (PEN) films. However, other films includethose having appropriate optical properties if radiation of the donor isperformed from the side opposite the receptor, including hightransmission of light at a particular wavelength as well as sufficientmechanical and thermal stability for the particular application. Incertain embodiments, the substrate may itself contain an imagingradiation absorber material, in which case a portion of the substratesuch as the top layer, or the whole substrate (e.g., if the absorber ishomogeneous throughout the substrate), can function as the LTHC layer.In that case, the substrate is optional in that the LTHC also functionsas a substrate.

The donor substrate, in at least some instances, is substantially planarso that uniform coatings can be formed. The typical thickness of thedonor substrate ranges from 0.025 millimeters (mm) to 0.15 mm,preferably 0.05 mm to 0.1 mm, although thicker or thinner donorsubstrates may be used.

Typically, the materials used to form the donor substrate and anyadjacent layer(s) can be selected to improve adhesion between the donorsubstrate and the adjacent layer(s), control temperature transportbetween the substrate and the adjacent layer, and control imagingradiation transport to the LTHC layer. However, an optional priminglayer can be used to increase uniformity during the coating ofsubsequent layers onto the substrate and also increase the bondingstrength between the donor substrate and adjacent layers. One example ofa suitable substrate with primer layer is Product No. M7Q (availablefrom DuPont Teijin Films, Osaka, Japan).

Optional Underlayer

An optional underlayer may be coated or otherwise disposed between adonor substrate and the LTHC layer to minimize damage to the donorsubstrate during imaging, for example. The underlayer can also influenceadhesion of the LTHC layer to the donor substrate element. Typically,the underlayer has high thermal resistance (i.e., a lower thermalconductivity than the substrate) and acts as a thermal insulator toprotect the substrate from heat generated in the LTHC layer.Alternatively, an underlayer that has a higher thermal conductivity thanthe substrate can be used to enhance heat transport from the LTHC layerto the substrate, for example to reduce the occurrence of imagingdefects that can be caused by LTHC layer overheating.

Suitable underlayers include, for example, polymer films, metal layers(e.g., vapor deposited metal layers), inorganic layers (e.g., sol-geldeposited layers and vapor deposited layers of inorganic oxides (e.g.,silica, titania, aluminum oxide and other metal oxides)), andorganic/inorganic composite layers. Organic materials suitable asunderlayer materials include both thermoset and thermoplastic materials.Suitable thermoset materials include resins that may be crosslinked byheat, radiation, or chemical treatment including, but not limited to,crosslinked or crosslinkable polyacrylates, polymethacrylates,polyesters, epoxies, and polyurethanes. The thermoset materials may becoated onto the donor substrate or LTHC layer as, for example,thermoplastic precursors and subsequently crosslinked to form acrosslinked underlayer.

Suitable thermoplastic materials include, for example, polyacrylates,polymethacrylates, polystyrenes, polyurethanes, polysulfones,polyesters, and polyimides. These thermoplastic organic materials may beapplied via conventional coating techniques (e.g., solvent coating orspray coating). The underlayer may be either transmissive, absorptive,reflective, or some combination thereof, to one or more wavelengths ofimaging radiation.

Inorganic materials suitable as underlayer materials include, forexample, metals, metal oxides, metal sulfides, and inorganic carboncoatings, including those materials that are transmissive, absorptive,or reflective at the imaging light wavelength. These materials may becoated or otherwise applied via conventional techniques (e.g., vacuumsputtering, vacuum evaporation, or plasma jet deposition).

The underlayer may provide a number of benefits. For instance, theunderlayer may be used to manage or control heat transport between theLTHC layer and the donor substrate. An underlayer may be used toinsulate the substrate from heat generated in the LTHC layer or toabsorb heat away from the LTHC layer toward the substrate. Temperaturemanagement and heat transport in the donor element can be accomplishedby adding layers and/or by controlling layer properties such as thermalconductivity (e.g., either or both the value and the directionality ofthermal conductivity), distribution and/or orientation of absorbermaterial, or the morphology of layers or particles within layers (e.g.,the orientation of crystal growth or grain formation in metallic thinfilm layers or particles).

The underlayer may contain additives, including, for example,photoinitiators, surfactants, pigments, plasticizers, and coating aids.The thickness of the underlayer may depend on factors such as, forexample, the material of the underlayer, the material and opticalproperties of the LTHC layer, the material of the donor substrate, thewavelength of the imaging radiation, the duration of exposure of thethermal transfer element to imaging radiation, and the overall donorelement construction. For a polymeric underlayer, the thickness of theunderlayer typically is in the range of 0.05 micron to 10 microns, morepreferably from about 0.1 micron to 4 microns, more preferably fromabout 0.5 micron to 3 microns, and more preferably from about 0.8 micronto 2 microns. For inorganic underlayers (e.g., metal or metal compoundunderlayer), the thickness of the underlayer typically is in the rangeof 0.005 micron to 10 microns, more preferably from about 0.01 micron to4 microns, and more preferably from about 0.02 micron to 2 microns.

A more detailed description of LITI donor underlayers is found in U.S.Pat. No. 6,284,425, which is incorporated herein by reference.

Light-to-Heat Conversion (LTHC) Layers

For radiation-induced thermal transfer, an LTHC layer is incorporatedwithin the thermal transfer donor to couple the energy of light radiatedfrom a light-emitting source into the thermal transfer donor. The LTHClayer typically includes an imaging radiation absorber material thatabsorbs incident radiation and converts at least a portion of theincident radiation into heat to enable transfer of the transfer layerfrom the thermal transfer donor to the receptor. In some embodiments,the thermal transfer element includes an LTHC layer and also includesadditional imaging radiation absorber material(s) disposed in one ormore of the other layers of the thermal transfer donor, for example thedonor substrate, a transfer layer, an optional interlayer, or anoptional release layer.

Typically, the imaging radiation absorber material in the LTHC layer (orother layers) absorbs light in the infrared, visible, and/or ultravioletregions of the electromagnetic spectrum, or within a particular range ofwavelengths. The imaging radiation absorber material is absorptive ofthe selected imaging radiation and present in the thermal transferelement at a level sufficient to provide an optical absorbance at thewavelength of the imaging radiation in the range of 0.2 to 3, andpreferably from 0.5 to 2. Typical radiation absorbing materials caninclude, for example, dyes (e.g., visible dyes, ultraviolet dyes,infrared dyes, fluorescent dyes, and radiation-polarizing dyes),pigments, organic pigments, inorganic pigments, metals, metal compounds,metal films, a ferricyanide pigment, a phthalocyanine pigment, aphthalocyanine dye, a cyanine pigment, a cyanine dye, and otherabsorbing materials.

Examples of typical imaging radiation absorber materials can includecarbon black, metal oxides, and metal sulfides. One example of a typicalLTHC layer can include a pigment such as carbon black, and a binder suchas an organic polymer. Another typical LTHC layer can include metal ormetal/metal oxide formed as a thin film, for example, black aluminum(i.e., a partially oxidized aluminum having a black visual appearance).Metallic and metal compound films may be formed by techniques, such as,for example, sputtering and evaporative deposition. Particulate coatingsmay be formed using a binder and any suitable dry or wet coatingtechniques.

Dyes typical for use as imaging radiation absorber materials in an LTHClayer may be present in particulate form, dissolved in a bindermaterial, or at least partially dispersed in a binder material. Whendispersed particulate imaging radiation absorber materials are used, theparticle size can be, at least in some instances, about 10 microns orless, and may be about 1 micron or less. Typical dyes include those dyesthat absorb in the IR region of the spectrum. Examples of such dyes aredescribed in the following: Matsuoka, M., “Infrared Absorbing Dyes,”Plenum Press, New York, 1990; Matsuoka, M., Absorption Spectra of Dyesfor Diode Lasers, Bunshin Publishing Co., Tokyo, 1990, U.S. Pat. Nos.4,722,583; 4,833,124; 4,912,083; 4,942,141; 4,948,776; 4,948,778;4,950,639; 4,940,640; 4,952,552; 5,023,229; 5,024,990; 5,156,938;5,286,604; 5,340,699; 5,351,617; 5,360,694; and 5,401,607; EuropeanPatent Nos. 321,923 and 568,993; and Beilo, K. A. et al., J. Chem. Soc.,Chem. Comm., 1993, 452-454 (1993), all of which are incorporated hereinby reference. IR imaging radiation absorber materials include thosemarketed by Glendale Protective Technologies, Inc., Lakeland, Fla.,under the designation CYASORB IR-99, IR-1 26 and IR-1 65. A specific dyemay be chosen based on factors such as solubility in and compatibilitywith a specific binder and/or coating solvent, as well as the wavelengthrange of absorption.

Pigmentary materials may also be used in the LTHC layer as imagingradiation absorber materials. Examples of typical pigments includecarbon black and graphite, as well as phthalocyanines, nickeldithiolenes, and other pigments described in U.S. Pat. Nos. 5,166,024and 5,351,617, incorporated herein by reference. Additionally, black azopigments based on copper or chromium complexes of, for example,pyrazolone yellow, dianisidine red, and nickel azo yellow can be useful.Inorganic pigments can also be used, including, for example, oxides andsulfides of metals such as lanthanum, aluminum, bismuth, tin, indium,zinc, titanium, chromium, molybdenum, tungsten, cobalt, iridium, nickel,palladium, platinum, copper, silver, gold, zirconium, iron, lead, andtellurium. Metal borides, carbides, nitrides, carbonitrides,bronze-nano-structured oxides, and oxides structurally related to thebronze family (e.g., WO₂) may also be used.

Metal imaging radiation absorber materials may be used, either in theform of particulates as described for instance in U.S. Pat. No.4,252,671, incorporated herein by reference, or as films as disclosed inU.S. Pat. No. 5,256,506, incorporated herein by reference. Typicalmetals include, for example, aluminum, bismuth, tin, indium, telluriumand zinc.

A particulate imaging radiation absorber material may be disposed in abinder. The weight percent of the imaging radiation absorber material inthe coating, excluding the solvent in the calculation of weight percent,is generally from 1 wt.% to 30 wt.%, more preferably from 3 wt. % to 20wt. %, and more preferably from 5 wt. % to 15 wt. %, depending on theparticular imaging radiation absorber material(s) and binder(s) used inthe LTHC.

LTHC layers known in the art generally include a UV-curable resin systemand a carbon black pigment dispersion as a small particle absorbermaterial. Carbon black is inexpensive, stable, easily processed, andabsorbs at the NIR imaging laser wavelengths of 808 nanometers (nm) and1064 nm. The spectral characteristics of carbon black generally resultin LTHC layers that are difficult to UV cure and difficult to inspectoptically during coating. In addition, the coatings are susceptible tothermal damage during the UV curing process due to the samelight-to-heat conversion process that occurs during laser thermalprinting. The UV lamp exposure includes power throughout the visible,where it is absorbed and converted to heat, even though the curingprocess is typically sensitized only in the UV. The result is oftenthermal damage and distortion of the film substrate.

Embodiments consistent with the present invention provide an LTHC layercontaining an imaging radiation absorber material and a radiationcurable material capable of being cured by exposure to radiation at acuring wavelength or wavelengths. In some embodiments the imagingradiation absorber material does not substantially increase radiationabsorption at a curing wavelength or within a range of curingwavelengths. For example, in some embodiments the imaging radiationabsorber material does not increase radiation absorbance at a curingwavelength or wavelengths by more than 50%, by more than 40%, by morethan 30%, by more than 20%, by more than 10%, or by more than 5%, wherethe lesser the increase in radiation absorbance is more preferred. Inother embodiments, the imaging radiation absorber material does notsubstantially increase radiation absorption at a curing wavelength orwithin a range of curing wavelengths prior to curing of the radiationcurable material, more preferably by not more than 10% prior to thecuring of the radiation curable material.

In other embodiments consistent with the present invention, an amount ofresidual unreacted curable material is substantially less than an amountof residual unreacted curable material present in a thermal transferelement having comparable optical density at the imaging wavelength andthickness in which the imaging radiation absorber material is replacedwith a small particle absorber material cured under the same conditions.For example, in some embodiments, the amount of unreacted curablematerial present, in comparison to the small particle absorber, is lessthan 50%, less than 40%, less than 30%, less than 20%, less than 10%, orless than 5%, where the lesser the amount of unreacted curable materialpresent is more preferred.

In other embodiments consistent with the present invention, an amount ofresidual unreacted curable material, after curing of the LTHC layer, issubstantially less than an amount of residual unreacted curable materialpresent in a thermal transfer element comprising a small particleabsorber material. For example, in some embodiments, the amount ofunreacted curable material present after curing of the LTHC layer, incomparison to the small particle absorber, is less than 50%, less than40%, less than 30%, less than 20%, less than 10%, or less than 5%, wherethe lesser the amount of unreacted curable material present is morepreferred.

An example of a small particle absorber material is carbon black asfound in UV Pastes such as 9B981 D, 9B950D and 9B923 from Penn Color(Doylestown, Pa.).

Suitable radiation curable materials include radiation curable monomers,oligomers, polymers and co(polymers), particularly acrylate andmeth(acrylate) monomers, oligomers, polymers and co(polymers).Preferably, the radiation source used to effect curing of the radiationcurable material emits radiation at a curing wavelength or wavelengthswithin the UV (200 nm-400 nm) or visible (400 nm-700 nm) radiationbands. In some embodiments, the radiation source used to effect curingmay be a laser or a flash lamp.

The use of an NIR dye or pigment as the imaging radiation absorbermaterial in the LTHC layer may offer a number of process and performanceadvantages in forming a radiation curable LTHC. First, many of thematerials are more efficient imaging radiation absorber materials at thelaser wavelength than other imaging radiation absorber materials thatabsorb significant radiation at a curing wavelength or wavelengths. Thiseffect translates to being able to use a lower imaging radiationabsorber material loading for a given laser power, potentially resultingin smoother surfaces. Second, the lack of substantial absorption in thevisible spectrum, for certain LTHCs, prevents unwanted light to heatconversion during UV exposure and reduces the likelihood for thermaldistortion of the coated film. Third, a more transparent spectral windowin the visible will lead to improvements in the optical inspectionprocess (detection of particulates and coating defects) during the LTHCand interlayer coatings, as well as during a final inspection of thedonor film at the manufacturing site, the customer site, or elsewhere.Fourth, greater transparency in the visible region of the spectrumallows for alignment of the laser system to a high resolution receptorsubstrate (e.g., a display backplane) through the donor film. Fifth,greater visible transparency also allows for alignment of apre-patterned donor film with a patterned receptor substrate. Finally, atransparent spectral window in the UV enables more efficient UV curing(lower residual concentration of unreacted radiation curable materials),shorter curing times (faster processing speeds), and lower UV lamp powersettings (less thermal damage to the coated film).

In order to better understand the benefits of the imaging radiationabsorber materials of the present invention in the LITI process,consider the optical properties in three spectral regions: the near-IR(NIR), visible (VIS), and ultraviolet (UV). The laser wavelength willtypically fall in the NIR spectral region (700 nm-1100 nm). In order tobe an efficient imaging radiation absorber material for a given type oflaser, the non-small particle absorber material typically must have asignificant absorption band at the laser wavelength. Preferred imagingradiation absorber material materials have effective extinctioncoefficients at the laser wavelength of at least 10³ mL/g-cm, preferably10⁴ mL/g-cm, and more preferably 10⁵ mL/g-cm.

Thus, examples of imaging radiation absorber materials suitable for usewith an 808 nanometer laser include Prussian Blue (Pigment Blue 27),copper phthalocyanine (Pigment Blue 15) and many of its substitutedderivatives, and polymethine dyes. Suitable near IR (NIR) imagingradiation absorbers also include solvent soluble cyanine dyes such asS0402, S0337, S0391, S0094, S0325, S0260, S0712, S0726, S0455 and S0728from FEW Chemicals (Wolfen, Germany); and YKR-2016, YKR-2100, YKR-2012,YKR-2900, D01-014 and D03-002 from Yamamoto Chemicals, Inc. (Tokyo,Japan) as well as soluble polymethine dyes such as Pro-Jet 830 LDI fromAvecia (Blackley, Manchester, UK). Other imaging radiation absorbersuseful in embodiments of the present invention include water solublecyanine dyes such as S0121, S0270 and S0378 from FEW Chemicals and bothsoluble and insoluble phthalocyanine imaging radiation absorbers such asYKR-1020, YKR-220, YKR-1030, YKR-3020, YKR-3071, YKR-4010, YKR-3030,YKR-3070, YKR-369, D05-003 and YKR-5010 from Yamamoto and Pro-Jet 800 NPand Pro-Jet 830 NP from Avecia.

FIGS. 2A-2C are graphs illustrating spectra of exemplary materials foruse in an LTHC layer. FIG. 2A is a graph illustrating a spectrum ofPrussian Blue (Penn Color) in an LTHC layer. FIG. 2B is a graphillustrating a spectrum of Pro-Jet 830 LDI (Avecia) in an LTHC layer.FIG. 2C is a graph illustrating a spectrum of YKR 2900 (Yamamoto) in anLTHC layer.

Increased transparency in the visible spectral region (400 nm-700 nm)can be important for both visual and/or optical inspection andalignment. In addition, it may lower the heat load on the LTHC layer andsubstrate during the UV-cure process, thus reducing substratedeformation and possible degradation due to thermal effects.

LTHC layers containing preferred NIR-imaging radiation absorbermaterials in the LTHC layer transmit at least 20% or more of theincident power in the visible region from an ideal light source having aflat spectral energy distribution over that same range at an LTHCabsorbance at the imaging wavelength of preferably 0.40 or greater, morepreferably 0.7 or greater, and most preferably 1.0 or greater. LTHClayers containing more preferred NIR-imaging radiation absorbermaterials transmit at least 30% or more of the incident power in thevisible region from an ideal light source having a flat spectral energydistribution over that same range at an LTHC absorbance at the imagingwavelength of preferably 0.40 or greater, more preferably 0.7 orgreater, and most preferably 1.0 or greater. LTHC layers containing morepreferred NIR-imaging radiation absorber materials transmit at least 40%or more of the incident power in the visible region from an ideal lightsource having a flat spectral energy distribution over that same rangeat an LTHC absorbance at the imaging wavelength of preferably 0.40 orgreater, more preferably 0.7 or greater, and most preferably 1.0 orgreater. LTHC layers containing more preferred NIR-imaging radiationabsorber materials transmit at least 50% or more of the incident powerin the visible region from an ideal light source having a flat spectralenergy distribution over that same range at an LTHC absorbance at theimaging wavelength of preferably 0.40 or greater, more preferably 0.7 orgreater, and most preferably 1.0 or greater.

In a similar fashion, the amount of UV energy (from approximately 200nm-400 nm wavelength) transmitted through the LTHC coating relates tothe ease with which the LTHC layer can be UV cured, ultimately affectingthe level of residuals, cure speed, and potential for thermal distortionof the LTHC layer. The LTHC coatings made using the NIR-imagingradiation absorber materials present at a level sufficient to achieve anabsorbance at the imaging wavelength of 0.2 to 3.0, in certainembodiments, do not show strong absorption through the accessibleultraviolet region (the polyester substrate effectively blocks all UVwavelengths below 300 nanometer) and transmit at least 15%, morepreferably 20%, and more preferably 25% or more of the incident power inthe ultraviolet region from an ideal radiation source having a flatspectral energy distribution over that same range. As a result, thecoatings can be cured with less total UV energy at higher line speedsand/or a lower UV lamp power setting to provide a cured LTHC layerhaving lower residuals and less thermal distortion.

As indicated, a particulate imaging radiation absorber material may bedisposed in a binder. The weight percent of the imaging radiationabsorber material in the coating, excluding the solvent in thecalculation of weight percent, is generally from 1 wt. % to 30 wt. %,more preferably from 3 wt. % to 20 wt. %, and more preferably from 5 wt.% to 15 wt. %, depending on the particular imaging radiation absorbermaterial(s) and binder(s) used in the LTHC.

Optional polymeric binders may be included in the LTHC layer. Suitablepolymeric binders for use in the LTHC layer include film-formingpolymers, for example, phenolic resins (e.g., novolac, cresol and resoleresins), polyvinyl butyral resins, polyvinyl acetates, polyvinylacetals, polyvinylidene chlorides, polyacrylates, cellulosic ethers andesters, nitrocelluloses, polycarbonates, polyesters, polyurethanes, andurethane acrylates. Other suitable binders may include monomers,oligomers, or polymers that have been or can be polymerized orcrosslinked. In some embodiments, the binder is primarily formed using acoating of polymerizable or crosslinkable monomers and/or oligomers withoptional polymer. When a polymer is used in the binder, the binderincludes 1 to 50 wt. %, preferably, 10 to 45 wt. %, polymer (excludingthe solvent when calculating wt. %).

Upon coating on the donor substrate, the monomers, oligomers, andpolymers are polymerized and/or crosslinked to form the LTHC layer. Insome instances, if crosslinking of the LTHC layer is too low, the LTHClayer may be damaged by the heat and/or permit the transfer of a portionof the LTHC layer to the receptor with the transfer layer.

The inclusion of a thermoplastic resin (e.g., polymer) may improve, inat least some instances, the performance (e.g., transfer propertiesand/or coatability) of the LTHC layer. A thermoplastic resin may improvethe adhesion of the LTHC layer to the donor substrate. In oneembodiment, the binder includes 25 to 50 wt. % (excluding the solventwhen calculating wt. %) thermoplastic resin, and preferably, 30 to 45wt. % thermoplastic resin, although lower amounts of thermoplastic resinmay be used (e.g., 1 to 15 wt. %). The thermoplastic resin is typicallychosen to be compatible (i.e., form a one-phase combination) with theother materials of the binder. A solubility parameter can be used toindicate compatibility, as described in Polymer Handbook, J. Brandrup,ed., pp. VII 519-557 (1989), incorporated herein by reference. In atleast some embodiments, a thermoplastic resin that has a solubilityparameter in the range of 9 to 13 (cal/cm³)^(1/2), preferably 9.5 to 12(cal/cm³)^(1/2), is chosen for the binder. Examples of suitablethermoplastic resins include polyacrylics, styrene-acrylic polymers andresins, and polyvinyl butyral.

Conventional coating aids, such as surfactants and dispersing agents,may be added to facilitate the coating process. The LTHC layer may becoated onto the donor substrate using a variety of coating methods. Apolymeric or organic LTHC layer is coated, in at least some instances,to a thickness of about 0.05 micron to about 20 microns, more preferablyof about 0.5 micron to about 10 microns, and more preferably of about 1micron to about 7 microns. An inorganic LTHC layer is coated, in atleast some instances, to a thickness in the range of 0.001 micron to 10microns, and preferably 0.002 micron to 1 micron.

Radiation absorber material can be uniformly disposed throughout theLTHC layer or can be non-homogeneously distributed. For example, asdescribed in U.S. Pat. No. 6,468,715, incorporated herein by reference,non-homogeneous LTHC layers can be used to control temperature profilesin donor elements. This can give rise to thermal transfer elements thathave improved transfer properties (e.g., better fidelity between theintended transfer patterns and actual transfer patterns).

LTHC layers can have a non-homogeneous distribution of absorbermaterial, for example, to control a maximum temperature attained in thedonor element and/or to control a temperature attained at the transferlayer interface. For example, an LTHC layer can have absorber materialdistribution that is less dense closer to the donor substrate and moredense closer to the transfer layer. In many instances, such a design cancause more radiation to be absorbed and converted into heat deeper intothe LTHC layer as compared to a homogeneous LTHC layer having the samethickness and optical density. For the sake of clarity, the term “depth”when used to describe a position in the LTHC layer means distance intothe LTHC layer in the thickness dimension as measured from the donorsubstrate side of the thermal mass transfer element. In other instances,it may be beneficial to have an LTHC layer having an absorber materialdistribution that is more dense closer to the donor substrate and lessdense closer to the transfer layer.

LTHC layers can also be formed by combining two or more LTHC layerscontaining similar or dissimilar materials. In this regard, where twomore LTHC layers are used, only one layer need contain an imagingradiation absorber material that does not substantially increaseradiation absorption at a curing wavelength. Other examples of LTHCconstructions are discussed in more detail below.

The thermal mass transfer donor elements can include a non-homogeneousLTHC layer. For example, the LTHC layer can have a distribution ofabsorber material that varies with thickness. In particular, the LTHClayer can have an absorber density that increases with increasing depth.More generally, the LTHC layer can be designed to have a varyingabsorption coefficient by varying the distribution or density of thesame absorber material throughout the LTHC layer, or by includingdifferent absorber materials or layers in different locations in theLTHC layer, or both. For the purposes of the present disclosure, theterm non-homogeneous includes anisotropic thermal properties ordistributions of material(s) in at least one direction in the LTHClayer.

In general, the absorption coefficient is proportional to the rate ofabsorption of imaging radiation in the LTHC layer. For a homogeneousLTHC layer, the absorption coefficient is constant through thethickness, and the optical density of the LTHC layer is approximatelyproportional to the total thickness of the LTHC layer multiplied by theabsorption coefficient. For non-homogeneous LTHC layers, the absorptioncoefficient can vary. Exemplary non-homogeneous LTHC layers have anabsorption coefficient that varies as a function of thickness of theLTHC layer, and the optical density will depend on the integral of theabsorption coefficient taken over the entire LTHC thickness range.

A non-homogeneous LTHC layer can also have an absorption coefficientthat varies in the plane of the layer. Additionally, absorber materialcan be oriented or non-uniformly dispersed in the plane of the LTHClayer to achieve an anisotropic thermal conductivity (e.g., acicularmagnetic particles can be used as absorber particles and can be orientedin the presence of a magnetic field). In this manner, an LTHC layer canbe made that conducts thermal energy efficiently through the thicknessof the layer to transport heat to the transfer layer while having poorthermal conductivity in the plane of the layer so that less heat isdissipated into adjacent, cooler areas, for example those areas thathave not been exposed to imaging radiation. Such an anisotropic thermalconductivity might be used to enhance the resolution of thermalpatterning using donor elements of the present invention.

Likewise, any of the other layers of a thermal mass transfer donorelement (e.g., substrate, underlayer, interlayer, and/or thermaltransfer layer) can be made to have anisotropic thermal conductivitiesto control heat transport to or away from other layers. One way to makelayers having anisotropic thermal conductivities is to have ananisotropic orientation or distribution of materials in the layer, thematerials having different thermal conductivities. Another way is imparta surface of one or more layers with a physical structure (e.g., to makea layer thinner in some spots and thicker in others).

By designing LTHC layers to have an absorption coefficient that varieswith layer thickness, imaging performance of the donor element can beenhanced. For example, the LTHC layer can be designed so that themaximum temperature attained in the donor element is lowered and/or thetransfer temperature (i.e., temperature attained at the transferlayer/LTHC interface or transfer layer/interlayer interface) is raised,relative to a homogeneous LTHC layer that has the same thickness andoptical density. Advantages can include the ability to use imagingconditions that can lead to improved transfer properties (e.g., transfersensitivity) without damaging the donor element or transferred patterndue to overheating of the donor.

In exemplary embodiments, thermal mass transfer donor elements includean LTHC layer that has an absorption coefficient that varies withthickness. Such an LTHC layer can be made by any suitable technique. Forexample, two or more layers can be sequentially coated, laminated, orotherwise formed, each of the layers having a different absorptioncoefficient, thereby forming an overall non-homogeneous LTHC layer. Theboundaries between the layers can be gradual (e.g., due to diffusionbetween the layers) or abrupt. Non-homogeneous LTHC layers can also bemade by diffusing material into a previously formed layer to create anabsorption coefficient that varies with thickness. Examples includediffusing an absorber material into a binder, diffusing oxygen into athin aluminum layer, and the like.

Suitable methods for making non-homogeneous LTHC layers include, but arenot limited to the following: sequentially coating two or more layersthat have absorber material dispersed in a crosslinkable binder, eachlayer having a different absorption coefficient, and either crosslinkingafter each coating step or crosslinking multiple layers together aftercoating all the pertinent layers; sequentially vapor depositing two ormore layers that have different absorption coefficients; andsequentially forming two or more layers that have different absorptioncoefficients, at least one of the layers including an absorber materialdisposed in a crosslinkable binder and at least one of the layers beingvapor deposited, where the crosslinkable binder may be crosslinkedimmediately after coating that particular layer or after other coatingsteps are performed.

Examples of non-homogeneous LTHC layers that can be made include thefollowing: a two-layer structure that has a higher absorptioncoefficient in a deeper region; a two-layer structure that has a lowerabsorption coefficient in a deeper region; a three-layer structure thathas an absorption coefficient that becomes sequentially larger withdepth; a three-layer structure that has an absorption coefficient thatbecomes sequentially smaller with depth; a three-layer structure thathas an absorption coefficient that becomes larger and then smaller withincreasing depth; a three-layer structure that has an absorptioncoefficient that becomes smaller and then larger with increasing depth;and so on depending on the desired number of layers. With increasingnumbers of regions having different absorption coefficients, and/or withthinner regions, and/or with increased diffusion between regions, anon-homogeneous LTHC layer can be formed that approximates acontinuously varying absorption coefficient.

In one embodiment, non-homogeneous LTHC layers that have an absorptioncoefficient that increases with depth can be used to lower a maximumtemperature attained in the LTHC layer and to increase the donor elementtransfer temperature when the donor element is irradiated from theshallow side of the LTHC layer. An advantage to decreasing a maximumtemperature in the donor element can be the reduction in defects causedby thermal decomposition or overheating of the LTHC layer or otherlayers. Such defects can include distortion of the transferred image,undesired transfer of portions of the LTHC layer to the receptor,unintended fragmentation of the transferred image, and increased surfaceroughness or other physical or chemical degradation of the transferredimage (e.g., due to mechanical distortion of one or more layers due tooverheating of the donor element during imaging). Such defects arereferred to collectively as imaging defects. Another advantage todesigning LTHC layers according to embodiments consistent with thepresent invention is that higher power radiation sources and/or longerdwell times (e.g., higher laser doses) can be used to raise the transfertemperature, thereby increasing the transfer fidelity while still notexceeding a temperature in the LTHC layer that might lead to imagingdefects.

LTHC layers according to embodiments consistent with the presentinvention may exhibit higher visible light transmission characteristicsthan corresponding LTHC layers containing small particle absorbermaterials or other imaging radiation absorber materials whichsubstantially absorb radiation at a curing wavelength or wavelengths.Some embodiments include a LITI donor film containing an LTHC layer thatis at least partially transparent to visible light. This allows foreasier visual or other on-line inspection of the LITI donor film fordefects during the manufacturing process, for example. In someembodiments, a LITI donor film is provided that is at least partiallytransparent to visible light, thus permitting precise alignment of apre-patterned donor film with a patterned receptor substrate andfacilitating fabrication of complex multilayer electronic devicesrequiring precise positioning of patterned layers.

The LTHC layer can be used in a variety of thermal transfer elements,including thermal transfer elements that have a multi-component transferassembly and thermal transfer elements that are used to transfer asingle layer of a device or other item. The LTHC layer can be used withthermal transfer elements that are useful in forming multilayer devices,as described above, as well as thermal transfer elements that are usefulfor forming other items. Examples include such items as color filters,spacer layers, black matrix layers, printed circuit boards, displays(e.g., liquid crystal and emissive displays), polarizers, z-axisconductors, and other items that can be formed by thermal transferincluding, for example, those described in U.S. Pat. Nos. 5,156,938;5,171,650; 5,244,770; 5,256,506; 5,387,496; 5,501,938; 5,521,035;5,593,808; 5,605,780; 5,612,165; 5,622,795; 5,685,939; 5,691,114;5,693,446; and 5,710,097; and PCT Patent Applications Nos. 98/03346 and97/15173.

Optional Interlayer

An interlayer may be included as an optional element in the thermaltransfer element. The optional interlayer may be used to minimize damageand contamination of the transferred portion of the transfer layer andmay also reduce distortion in the transferred portion of the transferlayer. The interlayer may also influence the adhesion of the transferlayer to the thermal transfer element or otherwise control the releaseof the transfer layer in the imaged and non-imaged regions. Typically,the interlayer has high thermal resistance and does not distort orchemically decompose under the imaging conditions, particularly to anextent that renders the transferred image non-functional. The interlayertypically remains in contact with the LTHC layer during the transferprocess and is not substantially transferred with the transfer layer.

Suitable interlayers include, for example, polymer films, metal layers(e.g., vapor deposited metal layers), inorganic layers (e.g., sol-geldeposited layers and vapor deposited layers of inorganic oxides (e.g,silica, titania, and other metal oxides)), and organic/inorganiccomposite layers. Organic materials suitable as interlayer materialsinclude both thermoset and thermoplastic materials. Suitable thermosetmaterials include resins that may be crosslinked by heat, radiation, orchemical treatment including, but not limited to, crosslinked orcrosslinkable polyacrylates, polymethacrylates, polyesters, epoxies, andpolyurethanes. The thermoset materials may be coated onto the LTHC layeras, for example, thermoplastic precursors and subsequently crosslinkedto form a crosslinked interlayer.

Suitable thermoplastic materials include, for example, polyacrylates,polymethacrylates, polystyrenes, polyurethanes, polysulfones,polyesters, and polyimides. These thermoplastic organic materials may beapplied via conventional coating techniques (e.g., solvent coating orspray coating). Typically, the glass transition temperature (T_(g)) ofthermoplastic materials suitable for use in the interlayer is 25° C. orgreater, more preferably 50° C. or greater, more preferably 100° C. orgreater, and more preferably 150° C. or greater. The interlayer may beoptically transmissive, optically absorbing, optically reflective, orsome combination thereof, at the imaging radiation wavelength.

Inorganic materials suitable as interlayer materials include, forexample, metals, metal oxides, metal sulfides, and inorganic carboncoatings, including those materials that are highly transmissive orreflective at the imaging light wavelength. These materials may beapplied to the light-to-heat-conversion layer via conventionaltechniques (e.g., vacuum sputtering, vacuum evaporation, or plasma jetdeposition).

The interlayer may provide a number of benefits. The interlayer may be abarrier against the transfer of material from the LTHC layer. It mayalso modulate the temperature attained in the transfer layer so thatthermally unstable and/or temperature sensitive materials can betransferred. For example, the interlayer can act as a thermal diffuserto control the temperature at the interface between the interlayer andthe transfer layer relative to the temperature attained in the LTHClayer. This may improve the quality (i.e., surface roughness, edgeroughness, etc.) of the transferred layer. The presence of an interlayermay also result in improved plastic memory or decreased distortion inthe transferred material.

The interlayer may contain additives, including, for example,photoinitiators, surfactants, pigments, plasticizers, and coating aids.The thickness of the interlayer may depend on factors such as, forexample, the material of the interlayer, the material of the LTHC layer,the material of the transfer layer, the wavelength of the imagingradiation, and the duration of exposure of the thermal transfer elementto imaging radiation. For polymer interlayers, the thickness of theinterlayer typically is in the range of about 0.05 micron to about 10microns, more preferably from about 0.1 micron to about 4 microns, morepreferably from about 0.5 micron to about 3 microns, and more preferablyfrom about 0.8 micron to about 2 microns. For inorganic interlayers(e.g., metal or metal compound interlayers), the thickness of theinterlayer typically is in the range of about 0.005 micron to about 10microns, more preferably, from about 0.01 micron to about 3 microns, andmore preferably from about 0.02 micron to about 1 micron.

Transfer Layer

A transfer layer may be included in the thermal transfer element. Atransfer layer is generally formed overlaying the LTHC layer, forexample, by evaporation or sputtering, by coating as a uniform layer, orby printing in a pattern using digital printing (e.g., digital inkjet ordigital electrophotographic printing), lithographic printing orevaporation or sputtering though a mask. As noted previously, otheroptional layers, for example, an optional interlayer, may be interposedbetween the LTHC layer and the transfer layer.

A transfer layer typically includes one or more layers for transfer to areceptor. These layers may be formed using organic, inorganic,organometallic, and other materials, including, for example, anelectroluminescent material or electronically active material. Althoughthe transfer layer is described and illustrated as having discretelayers, it will be appreciated that, at least in some instances, theremay be an interfacial region that includes at least a portion of eachlayer. This may occur, for example, if there is mixing of the layers ordiffusion of material between the layers before, during, or aftertransfer of the transfer layer. In other instances, two layers may becompletely or partially mixed before, during, or after transfer of thetransfer layer.

One example of a transfer layer includes a multi-component transferassembly that is used to form a multilayer device, such as an active orpassive device, on a receptor. In some cases, the transfer layer mayinclude all of the layers needed for the active or passive device. Inother instances, one or more layers of the active or passive device maybe provided on the receptor, the remaining layers being included in thetransfer layer. Alternatively, one or more layers of the active orpassive device may be transferred onto the receptor after the transferlayer has been deposited. In some instances, the transfer layer is usedto form only a single layer of the active or passive device or a singleor multiple layer of an item other than a device. One advantage of usinga multi-component transfer assembly, particularly if the layers do notmix, is that the important interfacial characteristics of the layers inthe multi-component transfer assembly can be produced when the thermaltransfer assembly is prepared and, preferably, retained during transfer.Individual transfer of layers may result in less optimal interfacesbetween layers.

The thermal transfer element can include a transfer layer that can beused to form, for example, electronic circuitry, resistors, capacitors,diodes, rectifiers, electroluminescent lamps, memory elements, fieldeffect transistors, bipolar transistors, unijunction transistors, metaloxide semiconductor (MOS) transistors, metal-insulator-semiconductortransistors, charge coupled devices, insulator-metal-insulator stacks,organic conductor-metal-organic conductor stacks, integrated circuits,photodetectors, lasers, lenses, waveguides, gratings, holographicelements, filters (e.g., add-drop filters, gain-flattening filters,cut-off filters, and the like), mirrors, splitters, couplers, combiners,modulators, sensors (e.g., evanescent sensors, phase modulation sensors,interferometric sensors, and the like), optical cavities, piezoelectricdevices, ferroelectric devices, thin film batteries, or combinationsthereof; for example, the combination of field effect transistors andorganic electroluminescent lamps as an active matrix array for anoptical display. Other items may be formed by transferring amulti-component transfer assembly and/or a single layer.

Examples of transfer layers that can be selectively patterned fromthermal mass transfer donor elements include transfer layers whichinclude colorants (e.g., pigments and/or dyes dispersed or dissolved ina binder), polarizers, liquid crystal materials, particles (e.g.,spacers for liquid crystal displays, magnetic particles, insulatingparticles, conductive particles), emissive materials (e.g., phosphorsand/or organic electroluminescent materials), hydrophobic materials(e.g., partition banks for ink jet receptors), hydrophilic materials,multilayer stacks (e.g., multilayer device constructions such as organicelectroluminescent devices), microstructured or nanostructured layers,photoresist, metals, polymer containing layers, adhesives, binders,enzymes or other bio-materials, or other suitable materials orcombination of materials. Examples of transfer layers are disclosed inthe following documents: U.S. Pat. Nos. 5,725,989; 5,710,097; 5,693,446;5,691,098; 5,685,939; and 5,521,035; International Publication Nos. WO97/15173, WO 98/03346, and WO 99/46961; and co-assigned U.S. patentapplication Ser. Nos. 09/231,724; 09/312,504; 09/312,421; and09/392,386.

Particularly well-suited transfer layers include materials that areuseful in optical devices suitable for display applications. Thermalmass transfer can be performed to pattern one or more materials on areceptor with high precision and accuracy using fewer processing stepsthan for photolithography-based patterning techniques and thus can beespecially useful in applications such as display manufacture. Forexample, transfer layers can be made so that, upon thermal transfer to areceptor, the transferred materials form color filters, black matrix,spacers, barriers, partitions, polarizers, retardation layers, waveplates, organic conductors or semi-conductors, inorganic conductors orsemi-conductors, organic electroluminescent layers (fluorescent and/orphosphorescent), phosphor layers, organic electroluminescent devices,organic transistors, and other such elements, devices, or portionsthereof that can be useful in displays, alone or in combination withother elements that may or may not be patterned in a like manner.

In some embodiments, the transfer layer is pre-patterned on the donorelement and all, or part, of the pre-patterned transfer layer istransferred to the receptor via the radiation induced imaging process.Various layers (e.g., an adhesion layer) may be coated onto the transferlayer to facilitate transfer of the transfer layer to the substrate.

LITI Patterning

For thermal transfer using radiation (e.g., light), a variety ofradiation-emitting sources can be used. For analog techniques (e.g.,exposure through a mask), high-powered light sources (e.g., xenon flashlamps and lasers) are useful. For digital imaging techniques, infrared,visible, and ultraviolet lasers are particularly useful. Suitable lasersinclude, for example, high power (e.g., ≧100 mW) single mode laserdiodes, fiber-coupled laser diodes, and diode-pumped solid state lasers(e.g., Nd:YAG and Nd:YLF). Laser exposure dwell times can be in therange from, for example, about 0.1 microsecond to 100 microseconds andlaser fluences can be in the range from, for example, about 0.01 J/cm²to about 1 J/cm².

When high spot placement accuracy is required (e.g., for highinformation full color display applications) over large substrate areas,a laser is particularly useful as the radiation source. Laser sourcesare compatible with both large rigid substrates such as 1 meter (m)×1m×1.1 mm glass, and continuous or sheeted film substrates, such as 100microns thick polyimide sheets.

Thermal Transfer to a Receptor

During imaging, the thermal transfer element is typically brought intointimate contact with a receptor for imaging and transfer of a portionof the transfer layer to the receptor. In at least some instances,pressure or vacuum may be used to hold the thermal transfer element inintimate contact with the receptor. A radiation source may then be usedto heat the LTHC layer (and/or other layer(s) containing imagingradiation absorber material) in an image-wise fashion (e.g., digitallyor by analog exposure through a mask) to perform image-wise transfer ofthe transfer layer from the thermal transfer element to the receptoraccording to a pattern in order to form, for example, an organicmicroelectronic device.

Typically, the transfer layer is transferred to the receptor withouttransferring any of the other layers of the thermal transfer element,such as the optional interlayer and the LTHC layer. Preferably, theadhesive and cohesive forces in the donor and receptor coatings areconfigured such that the transfer layer is transferred in the radiationexposed regions and is not transferred in the non-exposed regions. Insome instances, a reflective interlayer can be used to attenuate thelevel of imaging radiation transmitted through the interlayer and reduceany damage to the transferred portion of the transfer layer that mayresult from interaction of the transmitted radiation with the transferlayer and/or the receptor. This effect is particularly beneficial inreducing thermal damage that may occur when the receptor is highlyabsorptive of the imaging radiation.

During laser exposure, it may be desirable to minimize formation ofinterference patterns due to multiple reflections from the imagedmaterial, which can be accomplished by various methods. The most commonmethod is to effectively roughen the surface of the thermal transferelement on the scale of the incident radiation as described in U.S. Pat.No. 5,089,372. This roughening has the effect of disrupting the spatialcoherence of the incident radiation, thus minimizing self interference.An alternate method is to employ an antireflection coating within thethermal transfer element on either, or both, sides of the substrate. Theuse of anti-reflection coatings is known and may be implemented withquarter-wave thicknesses of a coating such as magnesium fluoride, asdescribed in U.S. Pat. No. 5,171,650, which is incorporated herein byreference.

Large thermal transfer elements can be used, including thermal transferelements that have length and width dimensions of a meter or more. Inoperation, a laser can be rastered or otherwise moved across the largethermal transfer element, the laser being selectively operated toilluminate portions of the thermal transfer element according to adesired pattern. Alternatively, the laser may be stationary and thethermal transfer element moved beneath the laser.

In some instances, it may be necessary, desirable, and/or convenient tosequentially use two or more different thermal transfer elements to forma device. For example, one thermal transfer element may be used to forma gate electrode of a field effect transistor and another thermaltransfer element may be used to form the gate insulating layer andsemi-conducting layer, and yet another thermal transfer layer may beused to form the source and drain contacts. A variety of othercombinations of two or more thermal transfer elements can be used toform a device, each thermal transfer element forming one or more layersof the device. Each of these thermal transfer elements may include amulti-component transfer assembly or may only include a single layer fortransfer to the receptor. The two or more thermal transfer assembliesare then sequentially used to deposit one or more layers of the device.In some instances, at least one of the two or more thermal transferelements includes a multi-component transfer assembly.

Receptors

The receptor substrate may be any item suitable for a particularapplication including, but not limited to, glass, transparent films,reflective films, metals, semiconductors, various papers, and plastics.For example, receptor substrates may be any type of substrate or displayelement suitable for display applications. Receptor substrates suitablefor use in displays such as liquid crystal displays or emissive displaysinclude rigid or flexible substrates that are substantially transmissiveto visible light. Examples of rigid receptor substrates include glass,indium tin oxide coated glass, low temperature polysilicon (LTPS), andrigid plastic.

Suitable flexible substrates include substantially clear andtransmissive polymer films, reflective films, non-birefringent films,transflective films, polarizing films, multilayer optical films, and thelike. Suitable polymer substrates include polyester base (e.g.,polyethylene terephthalate, polyethylene naphthalate), polycarbonateresins, polyolefin resins, polyvinyl resins (e.g., polyvinyl chloride,polyvinylidene chloride, polyvinyl acetals, etc.), cellulose ester bases(e.g., cellulose triacetate, cellulose acetate), and other conventionalpolymeric films used as supports in various imaging arts. Transparentpolymeric film base of 2 mils to 100 mils (i.e., 0.05 mm to 2.54 mm) ispreferred.

For glass receptor substrates, a typical thickness is 0.2 mm to 2.0 mm.It is often desirable to use glass substrates that are 1.0 mm thick orless, or even 0.7 mm thick or less. Thinner substrates result in thinnerand lighter weight displays. However, certain processing, handling, andassembling conditions may require thicker substrates. For example, someassembly conditions may require compression of the display assembly tofix the positions of spacers disposed between the substrates. Thecompeting concerns of thin substrates for lighter displays and thicksubstrates for reliable handling and processing can be balanced toachieve a preferred construction for particular display dimensions.

If the receptor substrate is a polymeric film, it may be preferred thatthe film be non-birefringent to substantially prevent interference withthe operation of the display in which it is to be integrated, or it maybe preferred that the film be birefringent to achieve desired opticaleffects. Exemplary non-birefringent receptor substrates are polyestersthat are solvent cast. Typical examples of these are those derived frompolymers consisting or consisting essentially of repeating,interpolymerized units derived from 9,9-bis-(4-hydroxyphenyl)-fluoreneand isophthalic acid, terephthalic acid or mixtures thereof, the polymerbeing sufficiently low in oligomer (i.e., chemical species havingmolecular weights of about 8000 or less) content to allow formation of auniform film. This polymer has been disclosed as one component in athermal transfer receiving element in U.S. Pat. No. 5,318,938. Anotherclass of non-birefringent substrates are amorphous polyolefins (e.g.,those sold under the trade designation Zeonex.TM. from Nippon Zeon Co.,Ltd.). Exemplary birefringent polymeric receptors include multilayerpolarizers or mirrors such as those disclosed in U.S. Pat. Nos.5,882,774 and 5,828,488, and in International Publication No. WO95/17303.

Various layers (e.g., an adhesive layer) may be coated onto the finalreceptor substrate to facilitate transfer of the transfer layer to thereceptor substrate. Other layers may be coated on the final receptorsubstrate to form a portion of a multilayer device. For example, anorganic light emitting diode (OLED) or other electronic device may beformed using a receptor substrate having a metal anode or cathode formedon the receptor substrate prior to transfer of the transfer layer fromthe thermal transfer element. This metal anode or cathode may be formed,for example, by deposition of a conductive layer on the receptorsubstrate and patterning of the layer into one or more anodes orcathodes using, for example, photolithographic techniques.

Microelectronic Device Fabrication with LITI Donors

A variety of electronic and optical devices can be fabricated usingradiation curable LITI donor films. In some instances, multiple thermaltransfer elements may be used to form a device or other object. Themultiple thermal transfer elements may include thermal transfer elementswith multi-component transfer assemblies and thermal transfer elementsthat transfer a single layer. For example, a device or other object maybe formed using one or more thermal transfer elements withmulti-component transfer assemblies and one or more thermal transferelements that transfer a single layer.

The multilayer device formed using the multi-component transfer assemblyof the transfer layer may be, for example, an electronic or opticaldevice. Examples of such devices include electronic circuitry,resistors, capacitors, diodes, rectifiers, electroluminescent lamps,electroluminescing devices, memory elements, field effect transistors,bipolar transistors, unijunction transistors, MOS transistors,metal-insulator-semiconductor transistors, charge coupled devices,insulator-metal-insulator stacks, organic conductor-metal-organicconductor stacks, integrated circuits, photodetectors, lasers, lenses,waveguides, gratings, holographic elements, filters (e.g., add-dropfilters, gain-flattening filters, cut-off filters, and the like),mirrors, splitters, couplers, combiners, modulators, sensors (e.g.,evanescent sensors, phase modulation sensors, interferometric sensors,and the like), optical cavities, piezoelectric devices, ferroelectricdevices, thin film batteries, or combinations thereof. Otherelectrically conductive devices that can be formed include, for example,electrodes and conductive elements.

Some embodiments consistent with the present invention provide atransfer layer that includes a multi-component transfer assembly used toform at least a portion of a passive or active device. As an example, inone embodiment the transfer layer includes a multi-component transferassembly that is capable of forming at least two layers of a multilayerdevice. These two layers of the multilayer device often correspond totwo layers of the transfer layer. In this example, one of the layersthat is formed by transfer of the multi-component transfer assembly isan active layer (i.e., a layer that acts as a conducting,semi-conducting, superconducting, waveguiding, frequency multiplying,light producing (e.g., luminescing, light emitting, fluorescing, orphosphorescing), electron producing, or hole producing layer in thedevice and/or as a layer that produces an optical or electronic gain inthe device.)

A second layer that is formed by transfer of the multi-componenttransfer assembly is another active layer or an operational layer (i.e.,a layer that acts as an insulating, conducting, semiconducting,superconducting, waveguiding, frequency multiplying, light producing(e.g., fluorescing or phosphorescing), electron producing, holeproducing, light absorbing, reflecting, diffracting, phase retarding,scattering, dispersing, or diffusing layer in the device and/or as alayer that produces an optical or electronic gain in the device). Themulti-component transfer assembly may also be used to form additionalactive layers and/or operational layers, as well as, non-operationallayers (i.e., layers that do not perform a function in the operation ofthe device but are provided, for example, to facilitate transfer of atransfer assembly to a receptor substrate and/or adhere the transferassembly to the receptor substrate).

The transfer layer may include an adhesive layer disposed on an outersurface of the transfer layer to facilitate adhesion to the receptor.The adhesive layer may be an operational layer, for example if theadhesive layer conducts electricity between the receptor and the otherlayers of the transfer layer, or a non-operational layer, for example ifthe adhesive layer only adheres the transfer layer to the receptor. Theadhesive layer may be formed using, for example, thermoplastic polymers,including conducting and non-conducting polymers, conducting andnon-conducting filled polymers, and/or conducting and non-conductingdispersions. Examples of suitable polymers include acrylic polymers,polyanilines, polythiophenes, poly(phenylenevinylenes), polyacetylenes,and other conductive organic materials such as those listed in Handbookof Conductive Molecules and Polymers, Vols. 1-4, H. S. Nalwa, ed., JohnWiley and Sons, Chichester (1997), incorporated herein by reference.Examples of suitable conductive dispersions include inks containingcarbon black, graphite, ultrafine particulate indium tin oxide,ultrafine antimony tin oxide, and commercially available materials fromcompanies such as Nanophase Technologies Corporation (Burr Ridge, Ill.)and Metech (Elverson, Pa.).

The transfer layer may also include an optional release layer disposedon the surface of the transfer layer that is in contact with the rest ofthe thermal transfer element, This release layer may partially orcompletely transfer with the remainder of the transfer layer orsubstantially all of the release layer may remain with the thermaltransfer element upon transfer of the transfer layer.

Although the transfer layer may be formed with discrete layers, it willbe understood that, in at least some embodiments, the transfer layer mayinclude layers that have multiple components and/or multiple uses in thedevice. It will also be understood that, at least in some embodiments,two or more discrete layers may be melted together during transfer orotherwise mixed or combined.

OLED Fabrication

The transfer of a multi-component transfer assembly to form at least aportion of an OLED provides an illustrative, non-limiting example of theformation of an active device using a thermal transfer element. Anexample of a multicomponent transfer unit is described in U.S. Pat. No.6,410,201, which is incorporated herein by reference. In at least someinstances, an OLED device includes a thin layer or layers of suitableorganic materials sandwiched between a cathode and an anode. Electronsare injected into the organic layer(s) from the cathode and holes areinjected into the organic layer(s) from the anode. As the injectedcharges migrate towards the oppositely charged electrodes, they mayrecombine to form electron-hole pairs which are typically referred to asexcitons. These excitons, or excited state species, may emit energy inthe form of light as they decay back to a ground state (see, e.g., T.Tsutsui, MRS Bulletin, 22, 39-45 (1997), incorporated herein byreference).

Illustrative OLED constructions are known to those skilled in the art(see, e.g., Organic Electroluminescence, Zakya Kafafi (ed.), CRC Press,NY, 2005). Illustrative examples of OLED constructions includemolecularly dispersed polymer devices where charge carrying and/oremitting species are dispersed in a polymer matrix (see J. Kido “OrganicElectroluminescent devices Based on Polymeric Materials”, Trends inPolymer Science, 2, 350-355 (1994), incorporated herein by reference),conjugated polymer devices where layers of polymers such aspolyphenylene vinylene act as the charge carrying and emitting species(see J. J. M. Halls et al., Thin Solid Films, 276, 13-20 (1996),incorporated herein by reference), vapor deposited small moleculeheterostructure devices (see U.S. Pat. No. 5,061,569 and C. H. Chen etal., “Recent Developments in Molecular Organic ElectroluminescentMaterials”, Macromolecular Symposia, 125, 1-48 (1997), incorporatedherein by reference), light emitting electrochemical cells (see Q. Peiet al., J. Amer. Chem. Soc., 118, 3922-3929 (1996), incorporated hereinby reference), and vertically stacked organic light-emitting diodescapable of emitting light of multiple wavelengths (see U.S. Pat. No.5,707,745 and Z. Shen et al., Science, 276, 2009-2011 (1997),incorporated herein by reference). The emission of light of differentcolors may be achieved by the use of different emitters and dopants inthe electron transport/emitter layer 206 (see C. H. Chen et al., “RecentDevelopments in Molecular Organic Electroluminescent Materials”,Macromolecular Symposia, 125, 1-48 (1997), incorporated herein byreference).

Other OLED multilayer device constructions may be transferred usingdifferent transfer layers. Furthermore, a separate emitter layer couldbe interposed between layers. The multilayer assembly can be transferredonto a receptor to form OLEDs. For example, green OLEDs can betransferred onto the receptor substrate. Subsequently, blue OLEDs andthen red OLEDs may be transferred. Each of the green, blue, and redOLEDs are transferred separately using green, blue, and red thermaltransfer elements, respectively, to form display sub-pixels.Alternatively, the red, green, and blue thermal transfer elements can betransferred on top of one another to create a multi-color stacked OLEDdevice of the type disclosed in U.S. Pat. No. 5,707,745, incorporatedherein by reference.

Another method for forming a full color device includes depositingcolumns of hole transport layer material and then sequentiallydepositing red, green, and blue electron transport layer/emittermulti-component transfer assemblies either parallel or perpendicular tothe hole transport material. Yet another method for forming a full colordevice includes depositing red, green, and blue color filters (eitherconventional transmissive filters, fluorescent filters, or phosphors)and then depositing multi-component transfer assemblies corresponding towhite light or blue light emitters.

After formation, the OLED is typically coupled to a driver and sealed toprevent damage. The thermal transfer element can be a small or arelatively large sheet coated with the appropriate transfer layer. Theuse of laser light or other similar light-emitting sources fortransferring these devices permits the formation of narrow lines andother shapes from the thermal transfer element. A laser or other lightsource could be used to produce a pattern of the transfer layer on thereceptor, including receptors that may be meters in length and width.

The following examples illustrate radiation curable LITI donor films andthe use of radiation cured thermal transfer elements according to someembodiments consistent with the present invention. One skilled in theart may appreciate some of the advantages of using radiation curablethermal transfer elements according to these embodiments. For example,the number of processing steps may be reduced as compared toconventional photolithography methods because many of the layers of eachOLED are transferred simultaneously, rather than using multiple etchingand masking steps. Moreover, the time required to produce patterned LITItransfer elements may be reduced. In addition, multiple devices andpatterns can be created using the same imaging hardware with differentthermal elements. EXAMPLES Term Meaning BAlQBis-(2-methyl-8-quinolato)-4-(phenyl-phenalato)- Aluminum, availablefrom H.W. Sands Corp, Jupiter, FL AlQ Tris(8-hydroxyquinoline) aluminumavailable from H.W. Sands Corp, Jupiter, FL LiF Lithium fluoride,99.85%, available from Alfa Aesar, Ward Hill, MA as product number 36359Al Puratronic aluminum shots, 99.999%, available from Alfa Aesar, WardHill, MA Ag Silver (target available from Arconium, Providence RI) ITOIndium tin oxide OEL Organic electroluminescent OLED Organiclight-emitting diode LCD Liquid Crystal Display RPM Revolutions perminute Irgacure 184 1-hydroxycyclohexyl phenyl ketone available fromCiba Specialty Chemicals Corporation, Tarrytown, NY, as Irgacure 184 PETPolyethylene terephthalate PEDOT VP A mixture of water and CH 80003,4-polyethylenedioxythiophene-polystyrenesulfonate (cationic) availablefrom H.C. Starck, Newton, MA Irgacure 3692-benzyl-2-(dimethylamino)-1-(4-(morpholinyl)phenyl) butanone, availablefrom Ciba Specialty Chemicals Corporation, Tarrytown, NY MEK MethylEthyl Ketone PMA 1-methoxy-2-propanol acetate PM 1-methoxy-2-propanol UVUltraviolet nm Nanometer kW Kilowatt μ Micrometer/micron AFM AtomicForce Microscopy TMPTA Trimethylolpropane triacrylate ester, availablefrom Sartomer, Exton, PA as SR351 LITI Laser-induced thermal imagingLTHC Light-to-heat conversion IL Interlayer Wt. % Weight percent HTM-001Hole transport material from Covion Organic Semiconductors, GmbH,Frankfurt, Germany TMM-004 Triplet Matrix Host Material from CovionOrganic Semiconductors, GmbH, Frankfurt, Germany M7Q PET film, 2.88 milthickness available from DuPont Teijin Films, Hopewell, VA OD OpticalDensity Esacure ONE difunctional alpha-hydroxyketone photoinitiatoravailable from Lamberti, Conshohocken, PA. TPO acylphosphine oxidephotoinitiator available from BASF, Charlotte, NC as Lucirin TPO

EXAMPLE 1

LTHC layers having similar absorptions at 808 nanometers were preparedcontaining carbon black and Prussian Blue (also known as Iron Blue andPigment Blue 27).

Run 1 was prepared in the following manner. Before application of theLTHC solution, the inside of the base film substrate, M7Q, 2.88 milthick polyethylene terephthalate (DuPont Teijin Films, Hopewell Va.),was corona treated using nitrogen at a linespeed of 50 feet per minuteand a power of 300 Watts. A Prussian Blue based LTHC solution (non-smallparticle absorber) having the composition shown in Table I was thenapplied onto the corona treated M7Q film using a reverse microgravurecoating method (Yasui Seiki Lab Coater, Model CAG-150). In order toachieve a dry thickness of approximately 2.8 microns, a line speed of 20feet/minute was used and a microgravure of 180R set at 9.0 feet perminute. The coating was dried in-line through a series of three ovens(75/75/80° C.) and photocured under ultraviolet (UV) radiation from aFusion UV Systems (Gaithersburg, Md.) 600 W/in. lamp with a D bulb at apower setting of 70%.

The cured coating had an optical density of approximately 2.7 at 670 nm.

Run 2 was prepared in the following manner. Interlayer solution I wasapplied onto the cured LTHC layer, Run 1, using a reverse microgravurecoating method (Yasui Seiki Lab Coater, Model CAG-150). In order toachieve a dry thickness of approximately 2.6 microns, a line speed of 20feet/minute was used and a microgravure of 180R set at 8.0 feet perminute. The coating was dried in-line through a series of three ovens(40/50/50° C.) and photocured under ultraviolet (UV) radiation usingfrom Fusion UV Systems 600 W/in. lamp with an H+ bulb at a power settingof 70%.

Run 3 was prepared in the following manner. Before application of theLTHC solution, the inside of the base film substrate, M7Q, 2.88 milthick polyethylene terapthalate (DuPont Teijin Films, Hopewell Va.), wascorona treated using nitrogen at a linespeed of 50 feet per minute and apower of 300 Watts. A carbon black based LTHC solution prepared using9B950D (small particle absorber) having the composition shown in Table Iwas then applied onto the corona treated M7Q film. The LTHC solution wasapplied using a reverse microgravure coating method (Yasui Seiki LabCoater, Model CAG-150). In order to achieve a dry thickness ofapproximately 2.8 microns, a line speed of 20 feet/minute was used and amicrogravure of 180R set at 32.1 feet per minute. The coating was driedin-line through a series of three ovens (75/75/80° C.) and photocuredunder ultraviolet (UV) radiation from a Fusion UV Systems 600 W/in. lampwith a D bulb at a power setting of 70%. The cured coating had anoptical density of approximately 2.6 at 670 nm.

Run 4 was prepared in the following manner. Interlayer solution I wasapplied onto the cured LTHC layer, Run 3, using a reverse microgravurecoating method (Yasui Seiki Lab Coater, Model CAG-150). In order toachieve a dry thickness of approximately 1.4 microns, a line speed of 20feet/minute was used and a microgravure of 200R set at 6.5 feet perminute. The coating was dried in-line through a series of three ovens(40/50/50° C.) and photocured under ultraviolet (UV) radiation from aFusion UV Systems 600 W/in. lamp with an H+ bulb at a power setting of70%.

Compositions of the two LTHC layer formulations are listed in Table Iand the dried films in Table II. Comparative property data for the LTHClayer coatings are presented in Table III. Extractable unreacted TMPTAwas determined using HPLC. Extracted unreacted total acrylates werecalculated from the measured TMPTA divided by the estimated percentageof TMPTA in the TMPTA monomer reported by Sartomer. The extractablesdata show how the increased UV transmission of the Prussian Blue LTHClayer (Run 1) and Prussian Blue LTHC layer with interlayer (Run 2) leadsto a better cure of the coating chemistry, dramatically reducing theamount of extractable TMPTA monomer compared to the carbon black LTHClayer (Run 3) and Carbon Black LTHC layer with interlayer (Run 4).

Surface roughness data from a Prussian Blue and a carbon black loadedLTHC layer and donor film were determined using tapping mode atomicforce microscopy (AFM) and Surface Interferometry. Tapping mode AFM areaprofiling on a 5 micron by 5 micron area was conducted using a DigitalInstruments Dimension 5000 SPM instrument. The root mean square (Rq)surface roughness was determined over the area with a resolution of 512by 512 pixels. Surface Interferometry was conducted using a Wyko NT3300optical profiler operating in VSI mode. The root mean square (Rq)surface roughness was determined on a size scale of 603 microns by 459microns. Root mean square values are reported in Table III for Runs 1,2, 3 and 4.

The increased surface roughness of the carbon black loaded LTHC layerrelative to the LTHC layer containing Prussian Blue as an imagingradiation absorber material is readily apparent. In addition, thesurface roughness of the Prussian Blue LTHC layer is almost identicalwith the interlayer coating as it is without the interlayer coating, incontrast to the performance of the carbon black loaded LTHC layer, whichexhibits high surface roughness before the interlayer is coated. Bothlower extractables and lower surface roughness can be advantageous toimproving thermal transfer efficiency and transferred image quality.

EXAMPLE 2

A series of LTHC layer coatings at different pigment loading levels wereprepared from the compositions shown in Table IV.

Run 5 was prepared in the following manner. Before application of theLTHC solution, the inside of the base film substrate, M7Q, 2.88 milthick polyethylene terapthalate (DuPont Teijin Films, Hopewell Va.), wascorona treated using nitrogen at a linespeed of 50 feet per minute and apower of 300 Watts. A Prussian Blue based LTHC solution using 9S928D(non-small particle absorber) having the composition shown in Table IVwas then applied onto the corona treated M7Q film. The LTHC solution wasapplied using a reverse microgravure coating method (Yasui Seiki LabCoater, Model CAG-1 50). In order to achieve a dry thickness ofapproximately 1.25 microns, a line speed of 20 feet/minute was used anda microgravure of 200R set at 6.2 feet per minute. The coating was driedin-line through a series of three ovens (75/75/80° C.) and photocuredunder ultraviolet (UV) radiation from a Fusion UV Systems 600 W/in. lampwith a D bulb at a power setting of 70%. The cured coating had anoptical density of approximately 0.682 at 670 nm.

Interlayer solution II was then applied onto the cured LTHC layer usinga reverse microgravure coating method (Yasui Seiki Lab Coater, ModelCAG-150). In order to achieve a dry thickness of approximately 1.16microns, a line speed of 20 feet/minute was used and a microgravure of200R set at 10.2 feet per minute. The coating was dried in-line througha series of three ovens (40/50/50° C.) and photocured under ultraviolet(UV) radiation from a Fusion UV Systems 600 W/in. lamp with an H+ bulbat a power setting of 70%.

Run 6 was prepared in the following manner. Before application of theLTHC solution, the inside of the base film substrate, M7Q, 2.88 milthick polyethylene terapthalate (DuPont Teijin Films, Hopewell Va.), wascorona treated using nitrogen at a linespeed of 50 feet per minute and apower of 300 Watts. A Prussian Blue based LTHC solution using 9S928D(non-small particle absorber) having the composition shown in Table IVwas then applied onto the corona treated M7Q film. The LTHC solution wasapplied using a reverse microgravure coating method (Yasui Seiki LabCoater, Model CAG-150). In order to achieve a dry thickness ofapproximately 2.75 microns, a line speed of 20 feet/minute was used anda microgravure of 180R set at 8.6 feet per minute. The coating was driedin-line through a series of three ovens (75/75/80° C.) and photocuredunder ultraviolet (UV) radiation from a Fusion UV Systems 600 W/in. lampwith a D bulb at a power setting of 70%. The cured coating had anoptical density of approximately 1.43 at 670 nm.

Interlayer solution II was then applied onto the cured LTHC layer usinga reverse microgravure coating method (Yasui Seiki Lab Coater, ModelCAG-150). In order to achieve a dry thickness of approximately 1.18microns, a line speed of 20 feet/minute was used and a microgravure of200R set at 10.2 feet per minute. The coating was dried in-line througha series of three ovens (40/50/50° C.) and photocured under ultraviolet(UV) radiation from a Fusion UV Systems 600 W/in. lamp with an H+ bulbat a power setting of 70%.

Run 7 was prepared in the following manner. Before application of theLTHC solution, the inside of the base film substrate, M7Q, 2.88 milthick polyethylene terapthalate (DuPont Teijin Films, Hopewell Va.), wascorona treated using nitrogen at a linespeed of 50 feet per minute and apower of 300 Watts. A Prussian Blue based LTHC solution using 9S928D(non-small particle absorber) having the composition shown in Table IVwas then applied onto the corona treated M7Q film. The LTHC solution wasapplied using a reverse microgravure coating method (Yasui Seiki LabCoater, Model CAG-150). In order to achieve a dry thickness ofapproximately 2.75 microns, a line speed of 20 feet/minute was used anda microgravure of 180R set at 7.9 feet per minute. The coating was driedin-line through a series of three ovens (75/75/80° C.) and photocuredunder ultraviolet (UV) radiation from a Fusion UV Systems 600 W/in. lampwith a D bulb at a power setting of 70%. The cured coating had anoptical density of approximately 3.127 at 670 nm.

Interlayer solution II was then applied onto the cured LTHC layer usinga reverse microgravure coating method (Yasui Seiki Lab Coater, ModelCAG-150). In order to achieve a dry thickness of approximately 1.16microns, a line speed of 20 feet/minute was used and a microgravure of200R set at 10.2 feet per minute. The coating was dried in-line througha series of three ovens (40/50/50° C.) and photocured under ultraviolet(UV) radiation from a Fusion UV Systems 600 W/in. lamp with an H+ bulbat a power setting of 70%.

Run 8 (comparative) was prepared in the following manner. Beforeapplication of the LTHC solution, the inside of the base film substrate,M7Q, 2.88 mil thick polyethylene terapthalate (DuPont Teijin Films,Hopewell Va.), was corona treated using nitrogen at a linespeed of 50feet per minute and a power of 300 Watts. A carbon black based LTHCsolution using 9B950D (small particle absorber) having the compositionshown in Table IV was then applied onto the corona treated M7Q film. TheLTHC solution was applied using a reverse microgravure coating method(Yasui Seiki Lab Coater, Model CAG-150). In order to achieve a drythickness of approximately 1.25 microns, a line speed of 20 feet/minutewas used and a microgravure of 180R set at 5.0 feet per minute. Thecoating was dried in-line through a series of three ovens (75/75/80° C.)and photocured under ultraviolet (UV) radiation from a Fusion UV Systems600 W/in. lamp with a D bulb at a power setting of 70%. The curedcoating had an optical density of approximately 0.46 at 670 nm.

Run 9 (comparative) was prepared in the following manner. Beforeapplication of the LTHC solution, the inside of the base film substrate,M7Q, 2.88 mil thick polyethylene terapthalate (DuPont Teijin Films,Hopewell Va.), was corona treated using nitrogen at a linespeed of 50feet per minute and a power of 300 Watts. A carbon black based LTHCsolution using 9B950D (small particle absorber) having the compositionshown in Table IV was then applied onto the corona treated M7Q film. TheLTHC solution was applied using a reverse microgravure coating method(Yasui Seiki Lab Coater, Model CAG-150). In order to achieve a drythickness of approximately 1.25 microns, a line speed of 20 feet/minutewas used and a microgravure of 200R set at 5.4 feet per minute. Thecoating was dried in-line through a series of three ovens (75/75/80° C.)and photocured under ultraviolet (UV) radiation from a Fusion UV Systems600 W/in. lamp with a D bulb at a power setting of 70%. The curedcoating had an optical density of approximately 0.95 at 670 nm.

The corresponding weight percentages in the cured films are listed inTable V. Table VI provides a comparison of the integrated visible andultraviolet light transmission characteristics for the coatings of TableV, containing representative NIR-imaging radiation absorber materials atvarious loadings, and two carbon black comparatives with a high and lowweight loading. Even at optical densities as high as 1.49 at the imaginglaser wavelength, where 97% of the incident radiation is absorbed, thetransmission in both the visible and UV regions of the non-smallparticle absorber LTHC layers is far superior to the carbon black loadedLTHC layers having a substantially lower absorption at the imaging laserwavelength.

EXAMPLE 3

A Prussian Blue LITI donor film, previously described as Example 2, Run7, containing a radiation cured thermal transfer element includingPrussian Blue pigment as an imaging radiation absorber materialdispersed at 21.6% pigment loading in a 2.75 micrometer thick LTHC wasused to pattern the emitting layer of an OLED device.

Receptor substrates were prepared on ITO-coated glass (0.7 mm thick)(ITO is available from ULVAC Technologies in Methuen, Mass. as S-ITO(150 NM)). The substrate was spin coated with Baytron P VP CH8000 (H. C.Starck, Newton, Mass.) in order to achieve a dry thickness ofapproximately 60 nm and then heated to 200° C. for 5 minutes in anitrogen purged oven. The coated substrate was then spin coated with asolution of HTM-001 (a hole transporting polymer from Covion OrganicSemiconductors GmbH, Frankfurt, Germany), and toluene while in an argonpurged glove box to achieve a dry thickness of approximately 100 nm.Finally, an approximate 20 nm layer of spiro-TAD (Covion OrganicSemiconductors GmbH, Frankfurt, Germany) was vacuum coated using astandard thermal evaporation procedure in a Balzers vacuum chamber at abackground pressure of 10⁻⁷ Torr on the top to finish the receptorstructure.

The LITI donor film, Example 2, Run 7 was vacuum coated using a standardthermal evaporation procedure in a Balzers vacuum chamber at abackground pressure of 10⁻⁷ Torr with co-evaporation of the host and dyecontrolled to achieve the desired 30 nm thick layers of TMM004, a Covionproprietary OLED host, doped with 9 weight percent Irppy (iridiumtris-phenyl pyridine(Irppy), a green phosphorescent dye). The host/dyesystem was subsequently transferred from the donor sheet to the receptorsurface using laser induced thermal imaging (LITI). The donor was imagedfrom the back side of the substrate using one single-mode Nd:YAG laserat a power of 1 watt at the imaging plane. Scanning was performed usinga system of linear galvanometers, with the laser beam focused onto theimage plane using an f-theta scan lens as part of a near-telecentricconfiguration. The laser spot size, measured at 1/e² intensity was18×250 microns. A unidirectional scan was used with a triangle ditherpattern and a frequency of 400 KHz. Requested linewidths were 110 micronwith a pitch of 165 microns. The transferred layer had good edgeroughness with no visible evidence of thermal damage or centerlinedefects.

Device fabrication was completed by successively vacuum coating thefollowing stack: Balq(100A)/Alq(200A)/LiF(7A)/Al(40A)/Ag(4000A) onto theLITI imaged receptor using a standard thermal evaporation procedure in aBalzers vacuum chamber at a background pressure of 10⁻⁷ Torr. Thedevices were encapsulated and tested for resultant light, current, andvoltage characteristics. The corresponding OLED device showed a peakluminance efficiency of 5.5 Cd/A and a voltage of 6.5 V at 200 nits.TABLE I Coating Formulations (Example 1) Non- Non- Small Small SmallSmall particle particle particle particle Interlayer Interlayer absorberabsorber absorber absorber Solution I Solution Component (g) (Wt %) (g)(Wt %) (g) II (g) Pigment Carbon Black 8 3.6 Prussian Blue 16 7.9Diluent TMPTA 92 41.6 84 41.6 49.5 99 Photoinitiator Irgacure 369 1 0.5TPO 2 1.0 Esacure ONE 0.5 1 Solvent PM acetate 45.4 20.5 37.5 18.6Isopropyl 74.7 33.8 62.5 30.9 31.3 62.6 acetate Isopropanol 18.7 37.4MEK 133.3 Wt % Solids 45.7 50.5 50 30

TABLE II Pigment Loading in Dry Film (Example 1) Small Non-Small Smallparticle Non-Small particle particle absorber particle absorberComponent absorber (g) (Wt %) absorber (g) (Wt %) Pigment Carbon Black 87.9 Prussian Blue 16 15.7 Diluent TMPTA 92 91.1 84 82.4 PhotoinitiatorIrgacure 369 1 1.0 TPO 2 2.0

TABLE III Summary of Carbon Black and Prussian Blue Donor Film Analyses(Example 1) LTHC/IL Surface Surface Interlayer Thickness ExtractedExtracted Roughness Roughness Run (IL) (SEM, TMPTA Acrylates* R_(q)R_(q) Identification Type μm) (μg/cm²) (μg/cm²) (25 μm²) (0.28 mm²) Run1 — 2.8 0.50 0.83 1.04 6.30 Run 2 TMPTA 2.8/2.6 0.14 0.23 0.70 4.95 Run3 — 2.8 2.32 3.87 0.88 15.40 Run 4 TMPTA 2.8/1.4 1.63 2.72 0.72 5.95*estimate based on 60 wt % TMPTA in raw material

TABLE IV Coating Compositions (Example 2) Run 5 Run 6 Run 7 Run 8 Run 9Component (g) (g) (g) (g) (g) Pigment Carbon Black 14.96 32.88 9S928D74.81 59.85 164.58 Diluent TMPTA 225.20 90.15 135.42 235.10 217.12Photoinitiator TPO 5.402 2.52 4.68 5.00 5.00 Solvent Isopropyl acetate202.5 101.3 202.5 156.20 140.40 Isopropyl 97.5 48.7 97.5 alcohol PMacetate 93.75 109.60 Wt % Solids 50.4 50.4 50.4 50.5 50.5

TABLE V Composition of Dry Films (Example 2) Run 5 Run 6 Run 7 Run 8 Run9 Component (Wt %) (Wt %) (Wt %) (Wt %) (Wt %) Carbon black 5.87 12.89Prussian Blue 9.80 15.70 21.61 TMPTA 88.43 82.65 76.86 92.17 85.15 TPO1.77 1.65 1.54 1.96 1.96

TABLE VI Integrated Visible and UV Transmission of LTHC Layers¹ (Example2) Imaging Radiation Imaging Absorber Integrated Integrated RadiationMaterial Visible Light UV Light Absorber Loading Absorbance TransmissionTransmission Material (Wt %) at 808 nm % T_(VIS) % T_(UV) PrussianBlue - 9.8 0.432 47.9 39.0 Run 5 Prussian Blue - 15.7 0.740 37.3 34.1Run 6 Prussian Blue - 21.6 1.49 25.6 25.1 Run 7 Carbon black - 5.9 0.4620.19 7.25 Run 8 Carbon black - 12.9 0.77 7.2 1.47 Run 9¹Visible range defined as 400-700 nanometers; ultraviolet range definedas 300-400 nanometers

1-44. (canceled)
 45. A thermal transfer element, comprising: asubstrate; a transfer layer; and a light-to-heat conversion layerdisposed between the substrate and the transfer layer to generate heatwhen the transfer element is exposed to imaging radiation, thelight-to-heat conversion layer comprising a cured material consistingessentially of a non-black body pigment, a diluent, and aphotoinitiator, wherein a material of the transfer layer is capable ofbeing imagewise transferred from the transfer element to a proximatelylocated receptor when the transfer element is selectively exposed toimaging radiation.
 46. The thermal transfer element of claim 45, whereinthe pigment comprises Prussian
 47. The thermal transfer element of claim45, wherein the light-to-heat conversion layer includes approximately15.7 wt. % of the non-black body pigment, approximalely 82.4 wt. % ofthe diluent, and approximately 2.0 wt. % of the photoinitiator.
 48. Athermal transfer element, comprising: a substrate; a transfer layer; andfirst and second light-to-heat conversion layers disposed between thesubstrate and the transfer layer to generate heat when the transferelement is exposed to imaging radiation, wherein at least one of thefirst and second light-to-heat conversion layers comprises a non-blackbody imaging radiation absorber material, and wherein the firstlight-to-heat conversion layer has a first absorption coefficient thatvaries as a function of a thickness of the first light-to-heatconversion layer and the second light-to-heat conversion layer has asecond absorption coefficient that varies in a plane of the secondlight-to-heat conversion layer, wherein a material of the transfer layeris capable of being imagewise transferred from the transfer element to aproximately located receptor when the transfer element is selectivelyexposed to imaging radiation.
 49. The thermal transfer element of claim48, wherein at least one of the first and second light-to-heatconversion layers has an anisotropic distribution of the absorbermaterial.
 50. The thermal transfer element of claim 48, wherein at leastone of the first and second light-to-heat conversion layers has avarying thickness.
 51. The thermal transfer element of claim 48, whereinat least one of the first and second light-to-heat conversion layersincludes magnetic particles.
 52. The thermal transfer element of claim48, wherein the transfer layer includes magnetic particles.
 53. Athermal transfer element, comprising: a substrate; a light-to-heatconversion layer applied over the substrate, wherein the light-to-heatconversion layer comprises a non-black body imaging radiation absorbermaterial, and wherein the light-to-heat conversion layer generates heatwhen file transfer element is exposed to imaging radiation; a transferlayer having a first surface applied to the light-to-heat conversionlayer and having a second surface opposite the first surface; and anadhesive layer applied to the second surface of the transfer layer,wherein the adhesive layer comprises an operational layer, wherein amaterial of the transfer layer is capable of being imagewise transferredfrom the transfer element to a proximately located receptor when thetransfer element is selectively exposed to imaging radiation.
 54. Thethermal transfer element of claim 53, wherein the adhesive layer iscapable of conducting electricity between the receptor and the transferlayer after the transfer to the receptor.
 55. The thermal transferelement of claim 53, wherein the adhesive layer comprises a conductingfilled polymer.
 56. The thermal transfer clement of claim 53, whereinthe adhesive layer includes a conductive dispersion comprising an inkcontaining one of carbon black, graphite, ultrafine particulate indiumtin oxide, and ultrafine antimony tin oxide.
 57. The thermal transferelement of claim 53, wherein the transfer layer includes conductiveparticles.
 58. A thermal transfer element, comprising: a substrate,wherein at least a portion of the substrate includes an imagingradiation absorber material; a light-to-heat conversion layer appliedover the substrate, wherein the light-to-heat conversion layer comprisesa non-black body imaging radiation absorber material, and wherein thelight-to-heat conversion layer generates heat when the transfer elementis exposed to imaging radiation; and a transfer layer applied over thelight-to-heat conversion layer, wherein a material of the transfer layeris capable of being imagewise transferred from the transfer element to aproximately located receptor when the transfer element is selectivelyexposed to imaging radiation.
 59. The thermal transfer element of claim58, wherein the imaging radiation absorber material in the substrate islocated only within a top layer of the substrate adjacent thelight-to-heat conversion layer.
 60. A thermal transfer element,comprising: a substrate, wherein the substrate has an anisotropicthermal conductivity; a light-to-heat conversion layer applied over thesubstrate, wherein the light-to-heat conversion layer comprises anon-black body imaging radiation absorber material and has ananisotropic thermal conductivity, and wherein the light-to-heatconversion layer generates beat when the transfer element is exposed toimaging radiation; and a transfer layer applied over the light-to-heatconversion layer, wherein the transfer layer has an anisotropic thermalconductivity, wherein a material of the transfer layer is capable ofbeing imagewise transferred from the transfer element to a proximatelylocated receptor when the transfer element is selectively exposed toimaging radiation.
 61. The thermal transfer element of claim 60, whereinthe light-to-heat conversion layer has a varying thickness.
 62. Thethermal transfer element of claim 60, wherein the transfer layer has avarying thickness.